Hashimoto’s thyroiditis and ablation-zone involution after microwave ablation for low-risk papillary thyroid carcinoma: An overlap-weighted cohort study

Abstract

Microwave ablation (MWA) is increasingly used for selected low-risk papillary thyroid carcinoma (PTC), but the influence of coexisting Hashimoto’s thyroiditis (HT) on post-ablation imaging involution remains unclear. To determine whether coexisting HT independently alters ablation-zone involution after MWA for low-risk PTC. Retrospective overlap-weighted cohort study. This study included 803 clinically euthyroid patients with biopsy-confirmed, single, unifocal low-risk PTC treated with MWA from August 2015 to March 2024. Patients were grouped according to HT status: PTC without HT (n=533) and PTC with HT (n=270). The primary endpoint was time to complete ablation-zone disappearance on ultrasound. Propensity-score overlap weighting, overlap-weighted generalized estimating equations, Kaplan-Meier analysis, and Cox models were used. Median follow-up was 12.0 months in the PTC group and 13.0 months in the PTC+HT group. Overlap weighting achieved excellent covariate balance. Complete ablation-zone disappearance occurred in 288 of 533 patients without HT (54.0%) and 120 of 270 patients with HT (44.4%). Using Kaplan-Meier time-to-event analysis, the estimated median time to complete disappearance was 14 months in the PTC group and 19 months in the PTC+HT group. HT was independently associated with slower disappearance (adjusted hazard ratio, 0.66; 95% CI, 0.53-0.82; p<0.001). Disease progression and complication rates did not differ significantly between groups. Coexisting HT delayed early ablation-zone involution after MWA for low-risk PTC but did not increase short-term disease progression or complications. Slow early volume reduction in patients with HT should be interpreted cautiously and should not be mistaken for residual tumor or treatment failure in the absence of suspicious enhancement or progressive growth.